The invention relates to a guide device for guiding elongated objects, particularly wires, which are movable in a passage direction along a passage axis relative to the guide device.
Elongated objects, such as metal wires, rods, bars or tubes, can be starting materials for high-value end products and are frequently subject to the highest quality requirements. Tests for surface defects are an important part of the quality control for such products. One objective is inter alia an uninterrupted and complete testing or inspection of the surfaces with high resolution, even for small defects, e.g. cracks, preferably in the cycle and speed of the manufacturing process. Nowadays such tests are frequently carried out using magnetic methods, particularly eddy current technology performed on a continuous basis, in which the object to be tested or inspected is guided at high speed through an axial test section of a test device e.g. equipped with a rotary test head with eddy current probes and the probes test the surface of the object, preferably in contactless manner.
In the passage direction upstream of the area of the test probes, such a test device normally has a so-called inlet nozzle and behind it an outlet nozzle. These guide devices, also known as protective nozzles fulfil a double function. They protect the test heads against damage, particularly during the entry and exit of the test material. They also limit the maximum eccentricity of the moving test material within the test section to a narrow, confined amount, within which the spacing compensation of the test device can cancel out the sensitivity fluctuations strongly dependent on the spacing between the test object surface and the test probe.
A guide nozzle known from DE 40 07 471 has for the damping of vibrations of the transiting objects a damping device with three guide elements directed onto the surface of the object and whereof each has a sliding body with wear-resistant surface for sliding contact with the test product and which is carried by a damping member made from a rubber-like material. Such test devices generally operate in a completely satisfactory manner.
However, particularly in the case of high passage or transit speeds and very thin, transiting testpieces, such as e.g. highly polished wires for the medical sector with diameters of approximately one or a few mm, very high disturbance levels have been observed, which impair the measuring accuracy. In addition, the metallic sliding bodies can damage sensitive surfaces.
The problem of the invention is to propose a guide device making it possible to increase the measuring accuracy of in particular test devices operating in contactless manner in the case of gentle material guidance.
According to the invention this problem is solved.
A guide device according to the invention can in particular be used with advantage in a test device for the preferably magnetic, non-destructive testing of elongated objects in a continuous process. It has a damping device for damping vibrations, particularly transverse vibrations of the transiting objects. The damping device has a plurality of elastic damping members for direct, preferably sliding contact with the transiting object and which are able to absorb vibration energy.
Such damping members acting directly on the test product and whereof there can be 10, 50, 100 or 1000, absorb vibration energy at numerous points, particularly in the range of maximum transverse deflection, i.e. in the area of a vibration antinode and have a damping counteracting effect on the object deflection. A large number of damping members can lead to each individual damping member acting on the test product only exerting a limited pressure force on the test product surface, so that the test product can be guided in a gentle manner. An advantageously statistical distribution of the damping members assists a damping in a wide, continuous vibration frequency spectrum. It has been found that in particular in the case of thin wires tested at high passage speeds wire vibrations can occur in the vicinity of the test probes, which give rise to high disturbance levels for the test signals and therefore impair the measuring accuracy, especially for the detection of small defects. A guide device with the inventive damping device guiding in surface-protecting manner can counteract such vibrations and ensure a particularly quiet running, with no or only limited transverse vibrations, of the test material in the vicinity of the test probes.
In a preferred embodiment, the damping device has a brush arrangement and is in particular formed by the latter. The bristles or fibers of a brush arrangement can engage in gently sliding manner on a transiting object and form the damping members. Vibrations of the object lead to a deflection, particularly a bending of fibers and/or a rubbing against one another of adjacent fibers deflected to a varying degree. Both the substantially elastic fiber bending and also the reciprocal rubbing of fibers require energy, which is deducted from a vibration of the object, so that its vibration is damped. Flexible bristles engaging gently on the guided object also facilitate the introduction and passage of the objects to be guided into or through the guide device and only very limited friction losses occur.
In addition to the damping action, a brush arrangement can also be used for cleaning a transiting object and/or it can act in the manner of a brush seal as a sealing device and seal the axial area following in the damping device transit direction against the introduction of dirt.
As a result of the flexibility of the bristle fibers, a single brush arrangement of given dimensions can be used for test objects of different diameters from an appropriate diameter range. There is an automatic diameter adaptation of the damping device in that, in accordance with the thickness of the transiting object, the bristle fibers are deflected or bent to a greater or lesser extent. Thus, it is e.g. possible to create guide devices with nominal sizes or internal diameters of e.g. between 1 mm and approximately 130 to 140 mm, each guide device with a brush arrangement being able to cover a certain diameter range of e.g. between 1 and 10 mm, particularly between 2 and 5 mm range width. A test device suitable for different diameters consequently only requires far fewer guide devices of this type than one having conventional guide devices.
As a function of the intended use the fibers can be hard or soft, thick or thin, more or less flexible, bending-resistant, buckling-resistant and/or abrasion-resistant. Thus, the fibers can be wire, synthetic or natural fibers. For guiding thin, particularly superfinished wires for the medical sector or other test objects having sensitive surfaces soft natural or synthetic fibers having a good sliding action on metals have proved very satisfactory. A brush arrangement can also have a uniform or statistical mixture of several different fibers or fiber types.
A brush arrangement can e.g. have at least one circular brush with e.g. substantially radially inwardly directed bristles. A preferred embodiment is characterized in that the brush arrangement has at least one and preferably several axially directed strip brushes distributed more particularly in symmetrical manner around the guide device surface. It is e.g. possible to provide three strip brushes in each case mutually displaced in the circumferential direction by 120xc2x0 and whose bristles define with their free ends an e.g. triangular passage for a transiting object. A circumferentially symmetrical arrangement of vibration-damping fibers with their free ends oriented radially and partly tangentially to the test object has proved to be particularly advantageous for vibration damping purposes. In addition, an improved centering of the transiting objects compared with conventional guide nozzles has been observed.
A format or diameter change is more particularly facilitated in a preferred embodiment in that the damping members or the at least one brush of the brush arrangement is fixed, preferably without tools, in detachable manner to a preferably sleeve-like brush support. A brush, which normally has a brush body, which carries the fibers or bristles, can in particular be inserted in the brush support, which makes a format or size change particularly simple.
Particularly good vibration damping can be achieved if the damping device has an active axial length which can be brought into contact with the transiting object and which represents a multiple, preferably 10 to 100 times, particularly approximately 30 times the diameter of the transiting object. A suitable, not excessively short length of the damping device is particularly suitable for damping different frequencies of a vibration spectrum.
In the axial direction, a damping device can be positioned upstream and/or downstream of the associated guide device. In a preferred embodiment the damping device is completely arranged in protective manner in the interior of the guide device casing or is integrated into the same. The guide device can have a front guide bush, upstream of the damping device and provided with a preferably cross-sectionally circular, axial passage opening, which is preferably widened in funnel-shaped manner on the inlet side. The object to be guided can be passed centrally through this passage opening into the interior of the damping device. A preferably provided, rear guide bush can follow the damping device and in particular in conjunction with the front guide bush can prevent a tilting of the transiting object in the guide device. The guide bushes can be shaped in the manner of drawing dies and/or are preferably made from wear-resistant hard metal. To prevent surface damage to the transiting material, preferably the inner face of the passage opening of a guide bush is highly polished at least in the area through which the object passes. A particularly inexpensive, simple construction of a guide device is obtained if the front and rear guide bushes have an identical construction.
According to a preferred embodiment, the first guide bush and/or the second guide bush are fixed detachably to a preferably sleeve-like casing of the guide device. A detachable fastening, which can e.g. be secured by screws, facilitates the replacement of guide sleeves with different passage opening diameters for adaptation to objects having different cross-sections, without it being necessary to replace the casing optionally fitted into a test device. Without separate fastening means such as screws or the like having to be provided for it, the damping device can be held in axially clearance-free manner and can optionally be axially fixed between the front guide bush and the rear guide bush.
The invention makes it possible to provide a test device operating with high measuring accuracy for preferably magnetic, non-destructive testing of elongated objects, particularly wires, in a continuous process. At least one test probe can operate in an axial test section of the test device. A test device according to the invention is characterized in that in the passage direction upstream and/or downstream of the axial test section is provided at least one guide device of the described type. Preferably the guide device is used in conjunction with a test probe, particularly an eddy current probe operating in contactless manner and which is constructed as a rotary probe or feed-through coil. Use with other, particularly magnetic testing methods, e.g. the stray flux method is also advantageous. Test objects running in a central, quiet and vibration-free manner are also advantageous in testing methods with test probes contacting the test object.
It has proved particularly advantageous for an axial spacing between the test probe and test device to be short, the axial spacing preferably being less than 10 mm, particularly between 0.5 and 2 mm. Such a close arrangement of a vibration-damping, protecting guide device upstream and/or downstream of the test probes ensures that no vibrations occur again between the guide device and the test probe section which could impair the measurement.
These and further features can be gathered from the claims, description and drawings and the individual features, both singly and in the form of sub-combinations, can be implemented in an embodiment of the invention and in other fields and can represent advantageous constructions.
An embodiment of the invention is described in greater detail hereinafter relative to the attached drawings, wherein show:
FIG. 1 A part sectional side view of an embodiment of an inventive guide device from a direction perpendicular to the passage direction of an elongated object.
FIG. 2 A cross-section perpendicular to the passage axis along line IIxe2x80x94II in FIG. 1.
FIG. 3 A side view (a) and an axial front view (b) of a damping device strip brush insertable in the guide device.
FIG. 4 A schematic side view of a test device provided with embodiments of guide devices upstream and downstream of a test probe.